Every day, billions of cells undergo apoptosis in the human body and are efficiently cleared, preventing the onset of inflammatory disease. Defects in the clearance of apoptotic cells have been identified in disease states, such as systemic lupus erythematosus and atherosclerosis, and have been implicated in the development of autoimmunity. The clearance of apoptotic cells depends on the ability of a phagocyte to locate and engulf the dying cell. These two processes are mediated by the so called "find-me" and "eat-me" signals, respectively, that are produced by apoptotic cells. My preliminary studies suggest that ATP accumulates in the extracellular medium during apoptosis, and can act as a "find-me" signal. It is unknown how extracellular ATP accumulates during apoptosis, or how this may influence the efficient clearance of apoptotic cells. In this proposal, I plan to determine the mechanism by which ATP accumulates in the extracellular medium of apoptotic cells, and the role that this plays in the efficient clearance of apoptotic cells. In Aim 1, we will use cell lines to examine the role of pannexin 1 hemichannels in the release of ATP during apoptosis, and the mechanism of pannexin 1 regulation during apoptosis. We will also examine the role of ecto-ATPase activity in the accumulation of extracellular ATP during apoptosis, as a possible contributory factor in the accumulation of ATP. In Aim 2, we will focus on how ATP may influence apoptotic cell clearance. Specifically, we will investigate how nucleotides in the apoptotic cell supernatants affect the ability of phagocytes to engulf apoptotic cells, by examining engulfment protein expression and phagocytic ability. We also aim to explore how nucleotides in the apoptotic cell supernatants may act on vascular endothelial cells to increase monocyte diapedesis to the affected area. Cells die during both normal and pathological processes, and are taken up efficiently by other cells. The clearance of dying cells is important for preventing inflammation, which is implicated as playing an important role in many disease processes including atherosclerosis and autoimmune disease. Understanding how dying cells promote their own clearance is an important issue with widespread implications.